Posted by Phillipa on June 14, 2013, at 18:52:29
Medscape Medical News > Psychiatry
Infection, Autoimmune Diseases Risk Factors for Mood Disorders
Jun 12, 2013
Severe infections requiring hospitalization and autoimmune diseases have been linked to an increased risk for subsequent mood disorders, new research shows.
Results of a large, longitudinal study showed that autoimmune disease increased the subsequent risk for a mood disorder diagnosis by 45%, and any history of hospitalization due to infection was associated with a 62% increased risk.
Furthermore, these 2 risk factors had a synergistic effect so that the risk for a subsequent mood disorder in individuals with an autoimmune disease and an infection more than doubled the risk for a subsequent mood disorder an effect that was larger than predicted by the combination of the single effects of the 2 disease groups.
"[A]utoimmune disease and the number of severe infections are independent and synergistic risk factors for mood disorders, with hospital-treated infections being the most common risk factor, with a population-attributable risk of 12% in this national cohort," the investigators, led by Michael E. Benros, MD, Aarhus University in Denmark, write.
The study was published online June 12 in JAMA Psychiatry.
Mood disorders and medical illnesses that involve inflammatory pathophysiologic mechanisms, such as cancer and cardiovascular disease, frequently co-occur, the authors note.
They add that recent human and animal research had linked mood disorders to inflammation and that proinflammatory cytokines and brain reactive antibodies can induce changes in neurotransmitter and neuroendocrine function related to psychiatric disorders.
However, although it has been hypothesized that immune responses might increase the risk for mood disorders, there have been no longitudinal studies examining a potential link between comorbid inflammatory illnesses and mood disorders.
To investigate the effect of autoimmune diseases and infection on the risk of developing mood disorders, the researchers conducted a nationwide, population-based, prospective cohort study that included 3.56 million individuals born in Denmark between 1945 and 1996.
Participants were followed up from January 1, 1977, through December 31, 2010, and hospitalization data for mood disorders, infection, and autoimmune disease were linked.
Of the total study population, 91,637 individuals were hospitalized for mood disorders. The researchers found that prior to a mood disorder diagnosis, 29,194 (31.9%) were diagnosed with 1 or more infections, and 4195 (4.6%) were diagnosed with 1 or more autoimmune diseases. In addition, 2113 were diagnosed as having an autoimmune disease and an infection.
The investigators report that a positive history of an infection, compared with its absence, was associated with an incidence rate ratio (IRR) for mood disorder of 1.63 (95% confidence interval [CI], 1.61 - 1.66).
A prior hospital contact due to an autoimmune disease was associated with an IRR for mood disorder of 1.45 (95% CI, 1.39 - 1.52).
In patients with prior hospital contact for an infection and an autoimmune disease, the IRR for a mood disorder diagnosis increased to 2.35 (95% CI, 2.25 - 2.46).
Most Common Risk Factor
The investigators point out that at 32%, infections were the most common risk factor. In contrast, autoimmune disease occurred in 5% of the population.
They note that the possible involvement of infections as a risk factor in the pathogenesis of mood disorders has previously only been investigated in a few small studies.
"Our results indicated that any history of hospitalization for infection increased the risk of mood disorders by 62%," they write.
The researchers add that because the registries only tracked hospital admissions, it "remains unclear" whether there is a link between less severe infections and mood disorders.
The findings support the hypothesis that there is a general immunologic response affecting the brain in a subpopulation of patients with mood disorders. However, the precise mechanism and whether this is a causal relationship is uncertain, the researchers note.
Søren Østergaard, MD, reports receiving 1 speaking fee, 1 consultant honorarium, travel support from Janssen-Cilag, and travel support from Bristol-Myers Squibb Company. The remaining investigators report no relevant financial relationships.
JAMA Psychiatry. Published online June 12, 2013. Abstract